What is the best initial response to jealousy?

I've experienced partner getting jealous of me for no reason, and the same in my past with previous relationship. I did not understand fully how badly it effected me with the ex til some time after my ex and I were through. With the ex I tried to remain calm, answer always thruthfully, being more concerned about his feelings than mine, making excuses for him.

My ex and partner don't reveal their jealousy the same way, but it gives me flashbacks and me feeling the same way as before.

It's been this mental struggle of trying to please and accomodate, and trying to revolt and protect my boundaries. I get introvert no matter as to me that kind of jealousy is a sign something's off. It is that anything can be twisted to look like something to fit their jealous agenda.

Both guys have in common that in the moment they act entitled to be jealous to afterwards act as if it never happened, but never any regard to how the jealousy has effected me. I learned with the ex that it always came back and not because something new that could be twisted around but actually when I thought we were happy, I know now it was a response to his feelings for me getting stronger to him getting scared, jealous I suppose.

If you are the one jealous of your partner what is the best, healthiest way to react to it? Have I been doing something wrong as in regard to my own reactions?

Updates
8 mo
The times they got jealous has been because some guy or guys were into me but I was not ever returning that, innocent flirting or what ever that was, and did behave myself always. I quit a job to get away. I did things to be less or not at all accesable. These were things I did on my own without asking my partner about it. I never rubbed it in my ex's or partners face. I tried to solve the situation without causing any harm. To me it seems how I respond make me look bad.
What is the best initial response to jealousy?
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